Testing integrated circuits to ensure their functionality and specification is accomplished with Automatic Test Equipment. As the capability of the integrated circuit improves, it is necessary that the capability of the test equipment improve, driving the cost of such equipment higher. It becomes increasingly more important to maximize the utilization of the equipment to keep the cost of test reasonable.
In testing logic integrated circuits, the number of pins that a tester is capable of testing has a direct impact on the cost of the tester. When purchasing a logic tester, the pin count of the tester is set by the integrated circuit that has the highest pin count.
In the logic integrated circuit business the number of units billed or sold is likely a normal distribution of its relation to pin count. This indicates that although a tester is specified and purchased by the highest pin count integrated circuit to be tested, the tester will be used a relatively small amount of time testing that specific integrated circuit. On the average most of the resources in a tester are not used most of the time. This makes very ineffective use of the high cost test equipment.
It is possible to improve the utilization of this type of test equipment by changing the test system architecture. If a 512 pin VLSI test system is purchased, but used the majority of time to test 128 pin integrated circuits, then 384 of the pins are idle most of the time. If the system were configured to utilize those 384 pins of resources in a way that it could also be testing three more 128 pin integrated circuits, tester utilization would be greatly improved. To achieve optimum improvement it is necessary to be able to test different logic integrated circuit types.
Prior art testers have attempted to solve these testing problems by physically combining smaller test heads into large pin count test heads, but these testers still have only one controller. There cannot be two completely independent test programs as they must time share the controller, as well as divide other common tester resources.